The invention concerns a method for regulating the temperature of an adjustable-crown roll, in which roll the roll mantle arranged to revolve around a stationary axle is loaded by passing a pressure fluid into a pressure chamber or series of chambers formed between the axle and the mantle so as to correct the deflection of the roll mantle, and which roll is respectively heated or cooled by passing heating or cooling fluid into the roll.
The invention further concerns an apparatus intended for carrying out the method in an adjustable-crown roll, which comprises a roll mantle arranged to revolve on a stationary axle by means of end bearings, the axle and roll mantle being sealed relative to one another by means of longitudinal seals such that, between the axle and the roll mantle, these longitudinal seals define a pressure chamber or a series of chambers, the deflection of the roll mantle being adjusted by means of the pressure of the pressure fluid supplied into the pressure chamber or series of chambers, and in which roll circulation devices are provided for heating/cooling fluid for regulation of the temperature of the roll.
In paper making machines, such rolls are commonly used to respectively form a dewatering press nip, a smoothing nip, or a calendering nip together with a backing roll. In these uses and also, e.g., in a supercalender, it is important that the distribution of the linear load, i.e. the profile, in the nip in the axial direction of the rolls can be made constant or that this profile can be regulated as desired, for example with a view to controlling the transverse moisture profile and/or thickness profile (caliper) of the web. For this purpose, in the prior art, several different adjustable-crown rolls are known, by means of which attempts are made to act upon the distribution of the linear load in a nip. As a rule, such rolls comprise a massive tubular, stationary roll axle and a roll mantle arranged to revolve around the roll axle. Between the axle and the mantle, a glide-shoe arrangement and/or a chamber or series of chambers of pressure fluid are fitted, which act upon the inner face of the mantle, so that the axial profile of the mantle at the nip can be straightened or adjusted as desired. The present invention is in particular related to such variable-crown rolls in which there is a chamber or series of chambers of pressure fluid between the roll axle and the roll mantle, the distribution of linear load of the roll being adjusted as desired by passing pressure fluid into this chamber or series of chambers.
In such rolls, one problem arises with the temperature profile of the roll. Especially in rolls in which the roll mantle is provided with a resilient coating, such as a polyurethane or rubber coating, it is important that the temperature level of the roll mantle should be sufficiently low and uniform. A uniform temperature promotes the formation of a uniform linear load as well as uniformity of the operation of the roll nip in the transverse direction of the web.
In the prior-art rolls of the type described above, attempts have been made to affect the roll temperature, e.g., cooling/heating fluid has been fed from one end of the roll into the pressure-fluid chamber therein, and the return-fluid duct has been provided at the opposite end of the roll. In such a roll, the temperature of the roll mantle is not uniform in the transverse direction of the roll, but rather the temperature of the roll mantle varies towards the other end of the roll, becoming higher or lower in a linear fashion, depending on whether cooling fluid or heating fluid is supplied into the pressure-fluid chamber. Additionally, attempts have been made to solve the problem of roll temperature such that, especially in rolls that require cooling, the cooling fluid has been passed into the pressure-fluid chamber, e.g., from two points. This has, however, had the consequence that the temperature distribution in the roll has been highly uneven. According to a third alternative, in prior-art apparatuses, temperature regulation has been arranged, in particular with respect to rolls about to be cooled, such that the cooling fluid has been passed into the pressure-fluid chamber in the roll at one end and removed through the opposite end, whereas the circulation of cooling fluid in the unpressurized chamber in the roll has been arranged in the opposite direction. This has, however, resulted in the substantial drawback that the temperature profile of the roll has been highly movable, which is an even more undesirable condition than a linear change in the temperature.